CRYSTRON ALARM is an alarm-equipped model from Citizen's Crystron series.
Model number: 50-2073
I like the design, which has the model name and button descriptions written directly on the rugged stainless steel body.

This model has an unusually shaped case back.
At first glance, it looks like a screw back, but there are no grooves on the inside, and it can actually be opened with a tool.
As expected, the previous owner is on the back cover?Is it a screw back opener?There were traces of a struggle.

When you open this back cover, you will see that there is an inner cover made of a smooth alumite-like material on the inside, and the outer cover and inner cover are not in close contact with each other, and the inner cover is directly visible through the hole in the screw back.
This structure, which has zero waterproof performance, seems to have a negative effect on the durability of the watch, but it may have been a last-ditch measure at the time to make the alarm sound as loud as possible by reverberating and amplifying it inside the watch.

For that reason, the alarm sound is surprisingly low, and it sounds more like a "chee-chee" than a "beep-beep".
Maybe it's just the one I have that isn't working.
I would like to get a dead stock product and compare the alarm sounds.

【postscript】
after that, I realized that I actually have the model that look different but are exactly the same inside, I compared the alarm sounds and found that it was a clear sound, so it seemed like the one I introduced this time was just not in good condition...